Handover (HO) indicates that a mobile station (MS) moves from an air interface of one base station to an air interface of another base station. Hereinafter, a handover procedure of a general IEEE 802.16 system will be described.
In an IEEE 802.16 network, a serving base station (SBS) may broadcast neighboring base station information through a neighboring advertisement (MOB_NBR-ADV) message in order to inform a mobile station (MS) of information (topology) about a basic network configuration.
The MOB_NBR-ADV message includes system information of a serving base station and neighboring base stations, for example, preamble indexes, frequencies, HO optimization degrees, downlink channel descriptor (DCD)/uplink channel descriptor (UCD) information, etc.
DCD/UCD information includes information necessary to enable an MS to perform information exchange in downlink and uplink. For example, DCD/UCD information includes HO trigger information, information about a medium access control (MAC) version of a base station, media independent handover (MIH) capability information, etc.
A general MOB_NBR-ADV message includes only information about neighboring base stations of an IEEE 802.16e type. Information about base stations of the types other than an IEEE 802.16e type may be broadcast to MSs through a service identity information advertisement (SII-ADV) message. Accordingly, an MS may request an SBS to transmit the SII-ADV message so as to acquire information about base stations of heterogeneous networks.
A procedure for performing handover by an MS, which acquires information about neighboring base stations using the above-described method, in an IEEE 802.16 network will be described in greater detail.
FIG. 1 is a diagram showing an example of a handover procedure which may be performed in an IEEE 802.16 system.
Referring to FIG. 1, first, a mobile station (MS) may access a serving base station (SBS) so as to perform data exchange (S101).
The SBS may periodically broadcast information about neighboring base stations (BSs) thereof to the MS through an MOB_NBR-ADV message (S102).
The MS may begin to scan candidate HO BSs using an HO trigger condition while communicating with the SBS. The MS may transmit a handover request (MOB_MSHO-REQ) message so as to request the SBS to perform a handover procedure if a handover condition exceeds, for example, a predetermined hysteresis margin value (S103).
The SBS may inform candidate HO BSs included in the MOB_MSHO-REQ message of the handover request from the MS through an HO-REQ message (S104).
The candidate HO BSs may take precautions for the MS which requests handover and transmit information associated with handover to the SBS through an HO-RSP message (S105).
The SBS may transmit information associated with handover acquired from the candidate HO BSs through the HO-RSP message to the MS through a handover response (MOB_BSHO-RSP) message. The MOB_BSHO-RSP message may include information for performing handover, such as an action time for performing handover, a handover identifier (HO-ID) and a dedicated HO CDMA ranging code (S106).
The MS may determine one target BS among the candidate HO BSs based on information included in the MOB_BSHO-RSP message received from the SBS. Then, the MS may attempt to perform ranging by transmitting CDMA code to the determined target BS (S107).
The target BS which receives the CDMA code may transmit information as to whether or not ranging is successfully performed and physical correction values to the MS through a ranging response (RNG-RSP) message (S108).
Next, the MS may transmit a ranging request (RNG-REQ) message for authentication to the target BS (S109).
The target BS which receives the ranging request message of the MS may provide system information available to the BS, such as a connection identifier (CID), to the MS through a ranging response message (S110).
If the target BS successfully completes authentication of the MS and sends all update information, the target BS may inform the SBS of the MS that handover is successfully performed through a handover completion (HO-CMPT) message (S111).
Thereafter, the MS may exchange information with the target BS which performs handover (S112).
The above-described handover procedure is performed between the MS and the BS which follow the IEEE 802.16e standard (WirelessMAN-OFDMA R1 Reference System). Hereinafter, in the present specification, for convenience, a system to which a general technology including the IEEE 802.16e standard is applied is referred to as a “legacy system”. An MS to which the legacy technology is applied is referred to as a “WirelessMAN-OFDMA R1 Reference MS”, an “YMS (Yardstick MS)” or a “legacy MS”, and a BS to which the legacy technology is applied is referred to as a “legacy BS”, a “R1 BS”, a “WirelessMAN-OFDMA R1 Reference BS” or an “YBS (Yardstick BS)”.
An MS to which an advanced technology including the IEEE 802.16m standard (WirelessMAN-OFDMA Advanced System) is applied is referred to as an “advanced MS” or an “AMS”, and a BS to which the advanced technology is applied is referred to as an “advanced BS” or an “ABS”. In addition, an operation mode of an MS or a BS to which the advanced technology is applied is referred to as an “advanced mode”.
It is assumed that an AMS accesses a YBS so as to receive a service from the YBS and an ABS (WirelessMAN-OFDMA R1 Reference System/WirelessMAN-OFDMA Advanced co-existing system) supporting both an AMS and a YMS exists adjacent to the YBS.
The YBS has only a legacy zone (LZone) having a physical channel frame structure applied to a legacy system. It is assumed that an ABS has only an advanced MS support zone (MZone: 16 M zone) having a physical channel frame structure applied to an advanced system if only an AMS is supported (WirelessMAN-OFDMA advanced system only). An ABS (WirelessMAN-OFDMA Reference System/WirelessMAN-OFDMA Advanced co-existing System legacy supportive) which supports both an AMS and an YMS has both a legacy zone (LZone) and an advanced MS support zone (MZone), which are divided in time units, for example, is divided using time division duplex (TDD) in frame units or subframe units, in uplink and downlink.
It is assumed that the AMS may receive services from both the ABS and the YBS. That is, it is assumed that the AMS may receive a service through any one of the new MS support zone and the legacy zone and may perform both a handover procedure defined in the legacy system and a handover procedure defined in the advanced system.
Generally, in order to perform handover from a serving YBS to an ABS supporting both an AMS and a YMS, the AMS may enter a legacy zone of the ABS and continue to receive a service in the legacy zone or perform zone switching to an advanced MS support zone. In addition, the AMS may perform handover by immediately performing zone switching to an advanced MS support zone without entering the legacy zone of the ABS.
Zone switching will now be described in detail. Zone switching refers to a procedure of enabling an AMS which operates in an LZone to operate in a resource region of an MZone in the case in which there are an LZone and an MZone divided using a TDD scheme in one carrier. That is, an IEEE 802.16e MAC operation is switched to an IEEE802.16m MAC operation. Zone switching includes movement of an AMS from an MZone to an LZone.
However, in order to guarantee service continuity when zone switching is performed, context mapping of a service flow identifier and mapping of a security association identifier (SAID) should be performed. In a general IEEE 802.16e/m system, context mapping of a service flow identifier may be automatically performed such that a first transport connection ID (CID) is mapped to a flow identifier (FID) in ascending order. However, since the type of a security association identifier (SAID) defined in the standard of the MZone and the type of an SAID defined in the standard of the LZone are different, the SAID may not be automatically mapped.
Accordingly, it is necessary to define a method of enabling a BS to inform an MS of how an SAID is mapped to a service flow identifier upon zone switching and to define a mapping rule of an SAID.